1. Field of the Invention
The present invention relates to a continuous heating device for coil springs that are formed in the shape of a coil by using a steel wire for a spring. More specifically, the present invention relates to a continuous heating device for coil springs, which provides an automated process for continuously heating coil springs through an electrical induction heating process in which the coil springs do not come in direct contact with a heat source while moving the coil springs by using a conveyor chain with a gradual increase in the rotational speed of the coil spring by using tapered rollers, and which drops the heated coil springs into a cooling tank that is filled with a cooling fluid, such as water or oil, to then be cooled in order to thereby improve the manufacturing productivity and the quality of the coil spring. In addition, the present invention further relates to a continuous heating method for coil springs, using the same device.
2. Description of the Prior Art
In general, the coil spring may be used as a buffer to absorb or accumulate energy by using an elastic force of the steel wire, or may be used for the purpose of securing operating functions of various mechanical components by using the restoring elasticity that is a repulsive force after compression.
Meanwhile, the most common type of coil spring is made by winding a steel wire in a spiral form, and the coil spring is manufactured through a basic inspection of a raw material, a surface peeling process, a heating process, a coil forming process, quenching, and tempering.
The coil spring, which has been manufactured as described above, is subject to a series of surface treatment processes in order to improve the mechanical properties of the coil spring and to increase the strength thereof. The surface treatment may be made through a tempering process, a shot peening process, a pre-treatment process, and a painting process after completing the forming and quenching processes of the coil spring. Thereafter, the product is output through a load testing process, a marking process, and a final inspection process.
Typically, the formed coil spring is input to the combustion heating furnace to then be heated about 980° C. or higher, which is higher than the A3 transformation point (the A3 transformation point of steel is 910° C.), for the heat treatment (quenching).
However, if the heat treatment process is automated to be a continuous process, it is difficult to evenly heat the entire area of the coil spring so that the decarburized portion (the portion of which the amount of carbon decreases on the surface due to the oxidization of the carbon on the surface into carbon monoxide when steel is heated in the air) of the coil spring, which is left on the surface of the material after the surface processing, may remain even after heating in order to thereby reduce the endurance life of the coil spring.
Korea Patent No. 10-0752224 discloses a high-frequency induction type heat treatment device for a shaft. According to the invention, a shaft is input between two rotational rollers for an automated continuous heat treatment of a shaft for automobile parts, and the shaft is moved by a conveyor chain while being rotated. Then, the shaft is heated by a high-frequency heating device that is installed in the intermediate position of the shaft movement path.
In the high-frequency induction heating type of heat treatment device for a shaft, a pair of rollers that are rotated on both sides of the lower portion of the shaft may be heated at the same time the shaft is heated so that the rollers exhibit a thermal expansion in the longitudinal direction thereof. Therefore, a high-frequency coil unit for the heat treatment is made to be very short in a ring shape and the shaft is immediately cooled by using a shaft cooling unit.
However, with the structure described above, since it takes a long time to sufficiently heat the shaft, the moving speed of the shaft may slow down so that the number of shafts that are produced per unit hour may decrease and the productivity may be dropped.
In addition, when the coil spring is input between a pair of rollers that are disposed to be parallel with each other in order to perform the heat treatment of the coil spring by using the high-frequency induction heating type of heat treatment device for a shaft, the coil spring may pop out in the rotational direction of the roller because the coil spring is shorter and lighter than the shaft. Therefore, it is difficult to apply the high-frequency induction heating type of heat treatment device to the coil spring.
An induction hardening process of a helical spring and a device thereof, which are disclosed in US Patent Publication No. 2008/0128057, provides a technique in which a helical spring is positioned on a mandrel and is induction-heated while the rotation of the spring is made by being moved on a caterpillar. However, the device has a complicated spring-input process and a complex mechanical configuration, and cannot significantly improve the productivity.
In addition, U.S. Pat. No. 8,912,472 discloses a device for heating a coil spring by using the electric induction heating method while rotating the coil spring on a pair of rotational rollers that are positioned to be parallel with each other to rotate in the same direction. However, when the coil spring is vertically dropped onto the rotational rollers for the input of the coil spring, the coil spring may pop out due to the rotation of the rollers. Furthermore, whenever the coil spring is dropped, the rotational rollers are to be opened wide. Therefore, the continuous heating device requires a complicated configuration and it is difficult to improve the productivity.
In addition, since the heating device has a structure of downwardly inputting the coil spring to the rotational rollers from above, which is suitable to be applied to a big coil spring, it is not suitable for manufacturing a small coil spring.